The shelf-life and utility of foodstuffs and silage, for instance, is often impaired by spoilage caused by yeasts and moulds. Yeasts and moulds may also present problems in the production of foodstuffs, and particularly in the brewing industry the adverse effects are great.
Sorbate and propionate in the form of various alkali salts have mostly been used for the inhibition of yeasts and moulds in foodstuffs. However, there is a tendency to cut back on the use of additives of this kind, and for instance the use of sorbate is prohibited in some European countries. The drawbacks of propionate include the fact that it does not always have a sufficient effect and the fact that it gives a flavour to foodstuffs. Since the consumer attitudes that are increasingly against the use of additives as well as the different foodstuff legislation in different countries must be taken into account, the industry has striven to find natural biopreservatives to replace such additives.
Lactic acid bacteria are known to produce various antimicrobial compounds, such as organic acids, hydrogen peroxide, diacetyl and bacteriocins, and one has attempted to use these as additives for instance to improve the shelf-life of foodstuffs. Commercially available is the product Nisaplin (Aplin & Barrett), comprising purified nisin produced by the bacterium Lactococcus lactis and having an effect on gram-positive bacteria only, and thus having no inhibitory effect on the growth of moulds and yeasts.
Efforts have been made to intensively increase the use of lactic acid bacteria for instance in the preservation of forage by testing combinations of lactic acid bacteria mainly with various enzyme preparations. However, such combinations do not have an inhibitory effect on the growth of yeasts and moulds, and therefore they have not provided a solution to the problems caused by yeasts and moulds.
European published application No. 0 302 300 discloses a process for preparing yeast and mould inhibiting products by culturing a Lactobacillus species and isolating the products excreted into the growth medium. These products are stated to be a complex mixture of low molecular weight (MW&lt;1000) compounds, and they are isolated from the growth medium by a multi-step process, which besides extraction steps to be carried out with butanol and ethanol comprises column chromatography and acetone precipitation or dialysis steps. Such a complicated process is not suitable for large-scale production. In said application, spores of Penicillium oxalicum are used to show the inhibitory effect.